The present invention relates to a porous filter pad or membrane for use in conjunction with a fluid pressure conveying system, such as a fluidized bed to assist in unloading bulk granular material particles into a flow line or trough.
Fluid pressure conveying systems for transferring or conveying bulk granular material particles from a storage chamber to a flow line or trough are well known. Storage chambers may be provided in various equipment including a hopper truck, hopper car, storage silo, bin, and in other in-plant uses and the like. Such storage chambers typically have fluidized beds where pressurized air is directed through an aeration pad or membrane to assist in conveying or transferring the bulk granular material particles from the storage chamber to a flow line or trough for unloading purposes. It is well known that the construction of such fluidized beds including the air permeable or aeration pad is very important in determining the speed and efficiency of the material unloaded.
The present invention is directed principally to the construction of a new and improved porous filter or aeration pad for use in conjunction with various types of fluid pressure conveying systems, some of which are described below in the typical environment in which such porous filter or aeration pad may be used.
The prior art is replete with various and different types of filter or aeration pads which have been constructed of various and different types of materials, made in one or several pieces and/or formed in a woven material construction. Examples of some different types of pads are shown, for example, in U.S. Pat. Nos. 4,355,928 and 4,568,244; although these patents are by no means an exhaustive disclosure of the prior art background showing the many and different types of filter or aeration pads that have been developed and/or have been used.
It will be apparent, however, that prior art filter or aeration pads or membranes have sought to provide constructions which not only serve to enhance high speed and efficiency, but which are also relatively economical, do not require extensive installation and maintenance cost, and do not require frequent replacement.
Typically, most filter or aeration pads currently in use are of some type of woven fabric construction to allow air to readily pass through the pad for the desired fluidization, while providing all of the foregoing features.
Some times the granular material particles can become impregnated in the woven fabric constructions, causing contamination and/or requiring cleaning. Water is typically used to clean the woven filter pads, and as can be expected, such pads require long drying time before they can be re-used, resulting in delay or interruption in changing over the fluid conveying system to a different product. Conventional woven fabric pads also usually have substantial back air pressure, that is, return of air back into the woven filter pad, resulting in lower overall efficiency and effectiveness in unloading granular material particles.
While porous filter pads, including those of woven construction, have worked quite well in the various environments in which they have been used, it will be understood, from the description of the present invention which is described in detail below, that there are numerous other areas of improvement possible which not only eliminate the disadvantages of prior art constructions, but which also provide new and improved features, operating conditions and better performance over prior art constructions, as will become apparent.